1. Field of the Invention
The present invention relates to a drive apparatus using a vibration-type actuator, an interchangeable lens, or an image pickup apparatus, for example, a drive apparatus of a vibration-type actuator suitable for driving a focus lens of a camera by using a wobbling operation.
2. Description of the Related Art
Various proposals have been made in terms of a vibration-type actuator capable of generating an elliptic motion on a particular point thereby driving an element (for example, see Japanese Patent Laid-Open No. 10-210775). FIG. 16 illustrates an example of a proposed structure.
As illustrated in FIG. 16, a vibrator of this vibration-type actuator includes an elastic element 1 made of a rectangular-shaped plate of a metallic material, and a piezoelectric element 2 bonded to a back surface of the elastic element 1. A plurality of protruding parts 3 are formed at particular positions on an upper surface of the elastic element 1. With this structure, when an alternate current (AC) voltage is applied to the piezoelectric element 2, a second-order bending vibration in a direction along longer sides of the elastic element 1 and a first-order bending vibration in a direction along shorter sides of the elastic element 1 occur simultaneously, which excite the protruding parts 3 to have an elliptic motion. In this situation, if there is a driven element 4 pressed into a contact with the protruding parts 3, the element 4 is driven linearly by the elliptic motion of the protruding parts 3.
The piezoelectric element 2 has two electrodes A1 and A2 separated from each other as illustrated in FIG. 17. When AC voltages V1 and V2 with an equal phase are applied to the two electrodes A1 and A2, a first-order bending vibration is excited such that the rectangular elastic element 1 has two nodes extending in the direction parallel to the longer sides as illustrated in FIG. 18A. When AC voltages V1 and V2 with opposite phases are applied to the two electrodes A1 and A2, a second-order bending vibration is excited such that the rectangular elastic element 1 has three nodes extending in the direction parallel to the shorter sides as illustrated in FIG. 18B. By exciting the elliptic motion on the protruding parts 3 by a combination of first-order and second-order bending vibrations (vibration modes) while pressing the driven element 4 into the contact with the protruding parts 3, it is possible to linearly drive the driven element 4.
The first-order bending vibration illustrated in FIG. 18A causes the protruding parts 3 to have a vibration whose amplitude varies in a direction perpendicular to a contact surface at which the driven element 4 is in contact with the protruding parts 3 (hereinafter such an amplitude will be referred to as a Z-axis amplitude). The second-order bending vibration illustrated in FIG. 18B causes the protruding parts 3 to have a vibration whose amplitude varies in a direction parallel to a direction in which the driven element 4 is driven (hereinafter such an amplitude will be referred to as an X-axis amplitude). Use of a combination of the first-order bending vibration and the second-order bending vibration makes it possible to excite the protruding parts 3 to have an elliptic motion as illustrated in FIG. 19. An ellipticity ratio of the elliptic motion is given by the ratio of the magnitude of the Z-axis amplitude and the magnitude of the X-axis amplitude. By changing the phase difference between the applied AC voltages V1 and V2, it is possible to change the magnitude of the X-axis amplitude. By changing the voltage amplitudes of the AC voltages V1 and V2, it is possible to change the magnitude of the Z-axis amplitude. Thus, it is possible to adjust the ellipticity ratio of the elliptic motion excited on the protruding parts 3.
By setting the frequency of the AC voltages applied to the piezoelectric element 2 so as to be closer to the resonance frequency of the vibrator, it is possible to increase the drive speed. By setting the frequency of the AC voltages applied to the piezoelectric element 2 so as to be more different from the resonance frequency of the vibrator, it is possible to reduce the drive speed. For example, in the basic structure of the vibration-type actuator illustrated in FIG. 16, there is a relationship between the drive frequency and the drive speed as shown in FIG. 20. That is, the actuator has a characteristic that the drive speed has its peak at the resonance frequency of the vibrator, and the drive speed decreases gradually as the drive frequency increases in a range higher than the resonance frequency but sharply as the drive frequency decreases in a range lower than the resonance frequency.
Thus, in the vibration-type actuator having such a characteristic, it is possible to control the speed (by the frequency) by changing the frequency of the two AC voltages V1 and V2 applied to the piezoelectric element 2. Furthermore, it is possible to control the speed (by the phase difference) by changing the phases of the AC voltages V1 and V2. Still furthermore, it is possible to control the speed (by the voltage) by changing the voltage amplitudes of the two AC voltages V1 and V2 applied to the piezoelectric element 2.
Thus, it is possible to control the speed of the vibration-type actuator by a combination of the control by the frequency, the control by the phase difference, and the control by the voltage.